In color printing, color images are produced on a print media by repeatedly superimposing on a single print sheet different image layers or color image separations. This is typically accomplished by a process wherein subsequent image layers are formed on subsequent passes of the photoreceptor, each writing a different image layer during a single revolution of the photoreceptor (single pass) or by employing multiple exposure devices each writing a different layer on different photoreceptors. The toned developed image is then transferred from the photoreceptor(s) to paper or similar material, and the toner image is fixed by heat and pressure (fusing) to form a permanent copy.
One major cause of image on paper (IOP) misregistration is from paper shrinkage due to fuser heating or enlargement due to stretching in some fuser designs. The effect of paper shrinkage/enlargement can be reduced by implementing an electronic registration process such as Contone High Resolution Image Path Electronic Registration (CHIPER), which compensates for the misregistration error caused by fuser shrinkage/stretching by adding/removing pixels to/from the image prior to printing.
The shrinkage/enlargement can be different in different directions, and could be of different forms, such as uniform shrinkage/enlargement, or spatially varying shrinkage/enlargement. It can be categorized into uniform and non-uniform components in each of a process and a lateral (x-process) direction. Non-uniform components can be further sub-divided into separable and non-separable portions. It is simpler and cheaper for the electronic registration process, such as CHIPER, to compensate for uniform and separable non-uniform error. A simple, hardware friendly design of the electronic registration process can perform well when the error is separable, i.e., the error in the process direction will be independent of the location in the lateral direction, and it does an effective job of reducing the error caused by fuser shrinkage/stretching to less than 0.05 mm. However, when an amount of residual error remains in the system after an electronic registration process, e.g. post CHIPER, the amount of IOP registration error can increase. Presently, there is a need to reduce the amount of registration error after an electronic registration process (e.g., post-CHIPER) to improve overall system IOP registration.
Accordingly, what is needed in this art are increasingly sophisticated methods for reducing the non-separable errors in IOP registration remaining in the system after an electronic registration process, such as CHIPER.